Conventionally as one of the fans which are capable of silent air-expelling operation, there is a multi-stacked circular plate fan X which is disclosed in Japanese laid-open publication 54-89602.
Such a multi-stacked plate fan provided with blades, as shown in FIGS. 25 and 26, substantially comprises a fan body 101 which is driven by a power operated-motor 100 which in turn is mounted on one end of a fan casing 110.
Upon operation of the power-operated motor 100, the fan body 101 is rotated so as to generate the air flow and expels the air from an air outlet 140.
Furthermore, as shown in FIG. 25, the fan body 101 comprises a multiplicity of thin annular circular plates 104 which are stacked together with a desired gap therebetween so that when the annular circular plates 104 are rotated, a shearing force is generated on the surface of these circular plates 104 in a circumferential direction. This shearing force works as a centrifugal force so as to generate an air flow thus providing a silent operation of the fan.
Furthermore, for providing a desired gap between the annular circular plates 104 and for making the flow of air from the inside to the outside smooth and increase the amount of air blow as shown in FIGS. 25 and 26, a plurality of arcuate blades 105 are disposed at a desired circumferential interval between the annular circular plates 104. The blades 105 also work as spacers.
However, the above mentioned multi-stacked plate fan X provided with blades still have following tasks to be resolved.
Namely, as shown in FIG. 26, every blade 105 has the trailing edge or the outermost outlet end extended to the outer peripheral portion of the annular circular plates 104. Therefore, at the outlet of the annular circular plates 104, as shown in FIGS. 26 and 27, a considerable distortion of velocity is generated in a circumferential direction and due to this distortion of velocity the pressure adjacent to the tongue portion of the casing fluctuates periodically thus generating the noise by rotation.
Furthermore, besides a tongue portion, during the course of rectifying the distortion of velocity, the turbulent flow is generated at the outer periphery of the annular circular plates 104, thus producing noise by the turbulant flow.
Furthermore, a portion of the air flow 106 which flows between the annular plates 104, 104 and locates at the rear portion of the blades 105 is peeled off so as to generate an air peeling-off region 108. Due to this peeling-off phenominon, a turbulent flow region 107 occurs at the outer periphery of the circular plate 104 and the turbulent flow noise is generated.
On the other hand, as shown in FIG. 26, the blade 105 has the leading edge or the inlet end thereof extended to the inner periphery of the circular plate 104.
Therefore, 1 as understood from the distribution curve of the absolute velocity 111 on the surface of the blade 105 as shown in FIG. 26, the velocity reduction ratio is greater on the inner end suction surface of the blade 105 than any other portion and, 2 the velocity reduction ratio at the inlet portion formed between the annular circular plates 104, 104 is greater than any other portion so that the air peeling-off phenominon is generated at the inner end suction surface of the blade 105. Furthermore, in case there is a velocity distortion relative to a circuferential direction at the inlet portion of the annular circular plates 104,104, an inflow angle of air toward the blade fluctuates and this also forms a part of the cause of the air peeling-off phenominon. Due to such a phenominon, a tubulence noise inside the annular circular plates 104, 104 also becomes greater.
Accordingly, it is an object of the present invention to provide a multi-stacked circular plate fan which can increase the amount of expelling air while assuring a silent fan operation.